Bone infections, such as osteomyelitis, can be debilitating or even fatal, and are notoriously difficult to treat. For example, osteomyelitis is an acute or chronic bone infection that may be caused by bacteria or fungi. The infection that causes osteomyelitis may start in another part of the body and spread to the bone through the blood. The infection may also spread to a bone from infected skin, muscles, or tendons next to the bone, as in osteomyelitis that occurs under a chronic skin ulcer (sore). Bone infection can also start after bone surgery, especially if the surgery is done after an injury or if metal rods or plates are placed in the bone. In children, the long bones are usually affected. In adults, the feet, spine bones (vertebrae), and the hips (pelvis) are most commonly affected.
Treatment of osteomyelitis is typically intended to prevent the infection from getting worse and ultimately to eliminate it from the body. The currently accepted treatment for osteomyelitis requires an extended period of intravenous antibiotics. Antibiotics are given to destroy the bacteria causing the infection. More than one antibiotic may be given at a time. The antibiotics are usually given intravenously, and must be taken for at least 4-6 weeks, sometimes longer. In some cases, surgery may be required in order to remove dead bone tissue, and open space left by the removed bone tissue may be filled with bone graft or packing material that promotes the growth of new bone tissue. If an orthopedic prosthesis is present near the site of infection, treatment may also require surgical removal of the prosthesis and infected tissue surrounding the area. A new prosthesis may be implanted in the same operation or delayed until the infection has gone away.
Chronic osteomyelitis may require amputation, especially in patients with diabetes or poor blood circulation. Furthermore, osteomyelitis may be particularly serious when it develops in patients having an implant or prosthesis. When bone becomes infected, pus produced within the bone may result in an abscess that limits the bone's blood supply. The lost blood supply can result in chronic osteomyelitis. This chronic infection can cause symptoms, including pain and disability, which persist for years.
Implants, and particularly silver-coated implants, have been suggested for use to control the spread of bacteria and the development of infection; however, such coatings have not proven effective. Silver coatings have been typically too limited to treat infected regions that are not immediately adjacent to the silver. In addition, the silver in most coatings elutes far too slowly to repel or inhibit colonizing bacteria. Although more quickly-eluting silver coatings have been described, such coatings typically do not last more than a few hours or days, and are not sufficient for the longer-term treatment usually required to treat osteomyelitis and similar infections. In particular, previously described devices are not capable of delivering a sustained level of silver ions to a large region of bone for a sufficient time period.
U.S. Pat. No. 6,500,165 to Frank describes one variation of an active antisepsis device that is intended to actively release silver from an implanted body site. However, this implant is limited by the delivery surface, and is not readily anchorable into a tissue that is already necrotic or damaged by infection, including infected bone tissue. US 2006/00004431 to Fuller et al. describes a similar device, having similar limitations.
Described below are implants that may address these problems and may be used to treat infections such as osteomyelitis. These devices may be implanted over an extended period even in bone or other tissue structures that are damaged or weakened by infection, and release silver ions and/or other antimicrobial or therapeutic substances.